A significant market opportunity exists in molded or shaped articles fabricated from wear resistant thermoplastic polymers and blends of thermoplastic polymers capable of functioning in high friction mechanical environments. M. P. Wolverton et al. in Machine Design, Feb., 1983, pp. 111-115, notes that the displacement of metals by thermoplastic materials in many gear and bearing applications is dependent upon performance and cost constraints. The article also notes that the property of thermoplastic articles to absorb shock and vibration and to operate at low noise and power consumption levels provides an advantage in such applications. The authors concluded that PEEK composites are particularly suited for elevated temperature applications and that a polyetherimide composite demonstrated flow at the same elevated temperature. PEEK with a Tm of 335.degree. C. was operative in a composite at 200.degree. C. and 260.degree. C. whereas the polyetherimide, which is amorphous, failed because of its low Tg.
Polyimides are a well known class of plastics. They are amply described by Kirk-Other, Encyclopedia of Chemical Technology, 3rd Ed., Vol. 18, pp. 704-719. C. Arnold, Jr., Journal of Polymer Science; Macromolecular Reviews, vol. 14, 265-378 (1979) devotes a portion of his article entitled: "Stability of High-Temperature Polymers," at pp. 322-333, to polyimides. The physical and chemical characteristics of polyimides have been well documented.
According to Alberino et al., U.S. Pat. No. 3,708,458, a polyimide of the reccurring unit formula ##STR2## "possesses highly useful structural strength properties but suffers the disadvantage that it has a relatively low glass transition point and, hence, relatively low resistance to loss of structural strength on exposure to high temperatures. Further, the polyimide in question is difficult to mold, by compression at elevated temperatures, because of its relatively poor flow properties in the mold." The patentees developed a polyimide to overcome to an extent these difficulties by including in the polymer backbone a certain proportion of the reaction product of 3,3',4,4'-benzophenone tetracarboxylic dianhydride with 2,4- or 2,6-toluene diamine (or the corresponding diisocyanates). The copolymers are regarded to have better flow properties in the mold by such difficult molding procedures as "sintering or hot pressing."
U.S. Pat. No. 3,652,409, to Mack et al., provides a bearing composition of polytetrafluoroethylene resins and a broad class of polyimide resins. Mack et al. note that "neither component alone, whether TFE resin or polyimide resin, has satisfactory bearing resistance particularly when moving against a soft metal such as brass."
Recently the processability of polyimides has been improved by blending or alloying them with other resins which are themselves more easily melt processable by virtue of being more easily thermoformed and injection molded. For example, U.S. Pat. No. 4,293,670 to Robeson et al., assigned to the present assignee, discloses blends of polyarylether resins and polyetherimide resins having excellent mechanical compatibility and good impact strength and environmental stress crack resistance. U.S. patent application Ser. No. 448,376 filed on Dec. 9, 1982 (now abandoned) in the name of J. E. Harris, assigned to the present assignee, involves blends of a poly(aryl ether), a poly(etherimide) polymer, a fiber, and a filler. U.S. patent application Ser. No. 537,042 filed on Sept. 29, 1983 (now abandoned) in the name of J. E. Harris et al., assigned to the present assignee, involves blends of a select polyarylketone and a polyetherimide. U.S. patent application Ser. No. 626,105 filed on June 29, 1984 in the name of J. E. Harris et al., assigned to the present assignee, involves blends of a polyamideimide and a poly(aryl ether ketone).
Over the years, there has been developed a substantial body of patent and other literature directed to the formation and properties of poly(aryl ethers) (hereinafter called "PAE"). Some of the earliest work such as by Bonner, U.S. Pat. No. 3,065,205, involves the electrophilic aromatic substitution (e.g. Friedel-Crafts catalyzed) reaction of aromatic diacylhalides with unsubstituted aromatic compounds such as diphenyl ether. The evolution of this class to a much broader range of PAE's was achieved by Johnson et al., Journal of Polymer Science, A-1, vol. 5, 1967, pp. 2415-2427, Johnson et al., U.S. Pat. Nos. 4,108,837 and 4,175,175. Johnson et al. show that a very broad range of PAE can be formed by the nucleophilic aromatic substitution (condensation) reaction of an activated aromatic dihalide and an aromatic diol. By this method, Johnson et al. created a host of new PAE's including a broad class of poly(aryl ether ketones), hereinafter called "PAEK's".
In recent years, there has developed a growing interest in PAEKs as evidenced by Dahl, U.S. Pat. No. 3,953,400; Dahl et al., U.S. Pat. No. 3,956,240; Dahl, U.S. Pat. No. 4,247,682; Rose et al., U.S. Pat. No. 4,320,224; Maresca, U.S. Pat. No. 4,339,568; Atwood et al., Polymer, 1981, vol 22, August, pp. 1096-1103; Blundell et al., Polymer, 1983 vol. 24, August, pp. 953-958, Atwood et al., Polymer Preprints, 20, no. 1, Apr. 1979, pp. 191-194; and Rueda et al., Polymer Communications, 1983, vol. 24, September, pp. 258-260. In early to mid-1970, Raychem Corp. commercially introduced a PAEK called STILAN.TM., a polymer whose acronym is PEK, each ether and keto group being separated by 1,4-phenylene units. In 1978, Imperial Chemical Industries PLC (ICI) commercialized a PAEK under the trademark Victrex PEEK. As PAEK is the acronym of poly(aryl ether ketone), PEEK is the acronym of poly(ether ether ketone) in which the 1,4-phenylene units in the structure are assumed.
Thus PAEKs are well known; they can be synthesized from a variety of starting materials; and they can be made with different melting temperatures and molecular weights. The PAEKs are crystalline, and as shown by the Dahl and Dahl et al. patents, supra, at sufficiently high molecular weights they can be tough, i.e., they exhibit high values (&gt;50 ft-lbs/in.sup.2) in the tensile impact test (ASTM D-1822). They have potential for a wide variety of uses, but because of the significant cost to manufacture them, they are expensive polymers. Their favorable properties class them in the upper bracket of engineering polymers.
PAEK's may be produced by the Friedel-Crafts catalyzed reaction of aromatic diacylhalides with unsubstituted aromatic compounds such as diphenyl ether as described in, for example, U.S. Pat. No. 3,065,205. These processes are generally inexpensive processes; however, the polymers produced by these processes have been stated by Dahl et al., supra, to be brittle and thermally unstable. The Dahl patents, supra, allegedly depict more expensive processes for making superior PAEK's by Friedel-Crafts catalysis. In contrast, PAEK's such as PEEK made by nucleophilic aromatic substitution reactions are produced from expensive starting fluoro monomers and thus would be classed as expensive polymers.
European Patent Application No. 125,816, filed Apr. 19, 1984, based for priority upon British Patent Application No. 8,313,110, filed May 12, 1983, is directed to a method for increasing the molecular weight by melt polymerization of a poly(aryl ether) such as PEEK.
The process of European Patent Application No. 125,816, provides a basis by melt polymerization above the crystalline melting point of the poly(aryl ether) to increase the molecular weight by chain extension of polymer blocks. The application theorizes that the procedure can be used for making the block copolymers described in U.S. Pat. Nos. 4,052,365 and 4,268,635. Implicit problems associated in the process of this application are the difficulty in controlling molecular weight of the resulting polymer and/or limiting isomerization and the problems associated with branching. The process of this European application would appear to be advantageous in making composites where the linearity and solution properties of the resulting polymer are not so critical.
PAEK block copolymers have been described in U.S. Pat. Nos. 4,052,365 and 4,268,635. U.S. Pat. No. 4,052,365 describes random or block copolymers having repeating units of the structure --Ar--O--Ar--CO and --Ar--O--Ar--SO.sub.2 --. The patent states that these block copolymers are crystalline. U.S. Pat. No. 4,268,635 describes a process for preparing polymers containing --Ar--O--Ar--SO.sub.2 -- and --Ar--O--Ar--CO-- units which the patentee believes to contain block structures. The patent states that the polymers are crystalline and exhibit improved high temperature properties compared with totally random copolymers of similar composition. However, the block copolymers in said patents require units with --SO.sub.2 -- linkages. The --SO.sub.2 -- linkage tends to break up the crystallinity of the polymer which results in inferior properties as compared to polymers which do not contain the --SO.sub.2 -- linkage but have ether and/or keto groups instead. Due to the amorphous nature of the sulfonyl containing component used in making these prior art block copolymers, lower rates of crystallization are induced and hence, their commercial utility is less than desirable. The --SO.sub.2 -- component so adversely affects the crystallinity properties that there is a maximum limit in the T.sub.m, far below that for the block polymers suitable for use in this invention. A further deficiency of these prior art block copolymers is that they cannot be used to form compatible blends with other PAEKs.